1. Field of the Invention
The present invention generally relates to primarily closed cell rigid foams useful for strengthening mechanical construction parts or for use as insulation material containing urethane groups, or urethane and isocyanurate groups, and more particularly to the polyol component used in preparing these foams.
2. Description of the Relevant Art
The preparation of cellular and non-cellular foams containing urethane groups and/or isocyanurate groups is well known.
An overview regarding the preparation and properties of polyurethane- (PU)- rigid foams is found, for example, in the Plastics Handbook Volume 7, Polyurethanes, edited by R. Vieweg and A. Hoechtlen, pgs 504 ff. (Verlag Carl Hanser, Munich, 1966). Polyisocyanurate (PIR) foams and/or modified PIR foams are described for example in Advances in Urethane Science and Technology, Volume 3, pgs. 141 ff and Volume 2, pgs. 241 ff. (Technomic Publishing Co., Inc., 1973 and 1974).
In preparing PU foams and/or PIR rigid foams routinely, aromatic polyisocyanates are reacted with higher molecular weight polyols, preferably polyether polyols or polyester polyols, in the presence of blowing agents, catalysts, flame retardants and other auxiliaries and additives. Also known is using mixtures of these starting components in place of the polyether polyols or polyester polyols. One important factor, in using mixtures of the starting components, was a cost reduction, which is achieved by mixing expensive, suitable, polyester polyols with economical polyether polyols in the preparation of high quality PU rigid foams. Suitable polyester polyols having a low viscosity, used in the preparation of PU rigid foams having good mechanical properties, are for example disclosed in DE-A 27 04 196. For preparing the polyester polyols, dicarboxylic acid mixtures comprising succinic, glutaric and adipic acids in certain quantity ratios are polycondensed with an isopropanol amine mixture and/or a hexanetriol isomeric mixture as well as with other lower molecular weight multivalent alcohols.
When using polyester polyols as a higher molecular weight polyhydroxyl compounds in the preparation of rigid foams containing urethane and isocyanurate groups, their flame resistance is improved and the brittleness is reduced. However, a disadvantage is that the polyester polyols are insufficiently miscible with the low boiling point halogenated hydrocarbons used as blowing agents due to their relatively high polarity in comparison to polyether polyols, preferably polyoxypropylene polyols. Especially when the polyurethane rigid foam formulations, affording flame resistant, containing isocyanurate groups, at a high isocyanate index, whose polyol component is predominantly difunctional polyester polyols, can one no longer dissolve sufficient quantities of halogenated hydrocarbon, blowing agent in the polyester polyol.
In order to overcome this disadvantage, the organic polyisocyanates are diluted for example with the low boiling point halogenated hydrocarbons. Also employed are chemically effective blowing agents, such as water or carboxyl group containing compounds, which react with isocyanates to form carbon dioxide.
Following the disclosure in DE A 29 35 402 (EPA 24 524), alkoxylated alkylphenols are used as solubility mediators for improving the compatibility of polyester polyols and halogenated hydrocarbons.
The objective of the present discovery was to prepare the most cost effective rigid foams containing urethane groups or urethane and isocyanurate groups having good mechanical properties, a high hydrolysis stability and particularly low densities, e.g. from 25 to 35 g/l in the absence of expensive solubility mediators which routinely worsen the mechanical properties
This objective was surprisingly met by the complete or partial use of polyester polyols with alkyl pendant groups as higher molecular weight polyol in the preparation of polyisocyanurate foams containing polyurethane groups and preferably urethane groups.